The present invention relates generally to hot water heaters and more particularly to a termally insulated water heater construction, a sealing device therefor, and a method of manufacturing the water heater.
Typically, water heaters are formed of an inner water tank with an outer shell located over the inner tank with an annular space therebetween. The space between the inner tank and outer shell is filled with a thermal insulation. For many years fiberglass has been used as the insulation material between the inner tank and outer shell. More recently, a foam such as urethane has been used as the thermal insulation material in place of fiberglass between the inner tank and outer shell. Typically, foamable material is injected into the space between the inner tank and outer shell, and is allowed to foam in situ. However, there is a problem in restraining the expanding foam within the annular space and more particularly within a predetermined location or region with the annular space. This specific locational confinement of the foam is important when using such foam insulation in a gas-fired water heater. In such an application it is extremely important to keep flammable foam away from the gas burner of the water heater. Over the years various proposals have been made to solve this problem.
U.S. Pat. No. 4,372,028 issued to Clark on Feb. 8, 1983 shows a water heater having a foam-filled closed collar located in the annular space between the inner tank and outer shell at the bottom of the inner tank, and the annular space above the collar filled with expanded foam. The collar functions as a stop to the expanded foam in the annular space thereabove. This patent further shows a method of manufacturing the water heater which includes the steps of forming a flexible, expandable closed elongated bag having a hole therein through which an expandable foam can be injected into the bag. The bag is filled with a foam material which expands the bag to form a collar, but before the foam material has had sufficient time to fully expand, the bag opening is sealed and the bag is circumferentially wrapped around the lower end of the tank with the bag ends overlapping each other. Next, and still before the foam material in the collar has had sufficient time to fully expand, the outer shell is positioned over the inner tank and bag. The foam in the bag continues expanding forming a collar which is in compression between the inner tank and outer shell. The annular space above the collar is then filled with expandable foam material.
U.S. Pat. No. 4,447,377 issued to Denton on May 8, 1977 shows a gas-fired water heater wherein a layer of fiberglass insulation material is wrapped around the bottom portion of the inner water tank around the combustion chamber and a plastic envelope is wrapped around the inner tank above the fiberglass insulation. The envelope is in the form of an elongated thin tube having an inner wall, an outer wall, a bottom wall, two end walls and an open top. When wrapped around the inner tank, the end walls of the envelope abut each other. The outer shell is positioned over the inner tank such that the envelope is in the annular space therebetween. Expandable foam is injected through the open envelope top into the envelope and allowed to expand therein.
U.S. Pat. No. 4,477,399 issued to Tilton on Oct. 16, 1984 shows a water heater having a inflatable toroidally shaped tube located around the bottom end of the inner tank such that when the toroidal tube is inflated with air, it seals the bottom end of the annular space between the inner tank and outer shell. A foamable material is then injected into the annular space above the toroidal tube to fill the annular space.
U.S. Pat. No. 4,875,272 issued to Nelson on Oct. 24, 1989 shows a water heater construction having a wedge-shaped member disposed between the inner water tank and the outer shell wherein the apex of the wedge is pointed in a downward direction and the base of the triangular shape opens upwardly into the annular clearance space between the tank and shell. This open base portion is designed so as to receive a portion of the liquid foam-in-place insulation which is used to insulate around the tank and between the shell such that as the material foams in place a force is exerted on the sides of the wedge due to the expanding foam thereby increasing the degree of interference between the sides of the wedge and the tank and shell.